Waveguide junction circulator having conductive partition in magnetic midplane of function

ABSTRACT

A junction of at least three standardized rectangular waveguides with a standard aspect ratio of about 2 : 1 comprises two spacedapart ferrite discs fixed to its inner wall surfaces in line with the junction axis. A metal plate transverse to this axis, parallel to the magnetic plane, partitions the junction substantially in its magnetic midplane and spans the whole area thereof, additional ferrite discs are fixed to each side of the plate to confront those on the junction walls. The assembly is equivalent to a stack of two junction circulators of reduced size which are electrically connected in series, exhibiting a greatly improved power-handling capability as compared with that of an unpartitioned junction circulator of the same overall dimensions.

United States Patent [191 Thai et al.

[ WAVEGUIDE JUNCTION CIRCULATOR HAVING CONDUCTIVE PARTITION IN MAGNETIC MIDPLANE OF FUNCTION [75] Inventors: Ngo IIai Thai; Joseph Violi, both of Paris, France [73] Assignee: Thomson-CSF, Paris, France [22] Filed: Nov. 26, 1973 [21] Appl. No.: 418,821

[30] Foreign Application Priority Data 3,714,608 l/l973 Barnes et al. 333/l.l

' Feb. 11, 1975 Primary Examiner-Paul L. Gensler Attorney, Agent, or Firm-Karl F. Ross; Herbert Dubno 57] ABSTRACT A junction of at least three standardized rectangular waveguides with a standard aspect ratio of about 2 z 1 comprises two spaced'apart ferrite discs fixed to its inner wall surfaces in line with the junction axis. A metal plate transverse to this axis, parallel to the magnetic plane, partitions the junction substantially in its magnetic midplane and spans the whole area thereof, additional ferrite discs are fixed to each side of the plate to confront those on the junction walls. The assembly is equivalent to a stack of two junction circulators of reduced size which are electrically connected in series, exhibiting a greatly improved powerhandling capability as compared with that of an unpartitioned junction circulator of the same overall dimensons.

7 Claims, 6 Drawing Figures PATENTEU H975 3,866,150

saw 10F 3 PRIOR ART 1 PATENTEU 1 I975 7 ,866,150

sum 2 or 3 PATENTEU F551 1 5 SHEET 3 3 PIC-3.6

BACKGROUND OF THE INVENTION The present invention relates to improvements in circulators-of the type wherein three coplanar waveguide arms of rectangular cross-section merge in a magneticplane junction.

As generally defined, a circulator is a microwave component with a metallic structure, having a certain number of openings or ports, which transmits the energy which it receives through one port to another port. The component also has the property of nonreciprocity, that is to say, if the direction from which the incident energy arrives is changed, the entry and exit functions of the ports are not interchanged. This state of non-reciprocity is brought about by using ferrites in a component of this type. Ferrites are ceramic magnetic materialsformed chiefly of metal oxides, but they differ from conventional metallic magnetic materials by reason of the fact that they are non-conductors and have low hysteresis losses at microwave frequencies.

Circulators are divided into three classes. A first class comprises circulators which operate on the principle of rotating the plane of polarization of a wave, the rotation being brought about by the Faraday effect caused by a ferrite rod to which a longitudinal external mag netic field is applied.

A second class comprises so-called phase-shift circulators which consist of a combination of, for example, a magic T, two 90 phase-shifters employing a nonreciprocal ferrite, and a 3-dB coupler. This type of circulator is used in mediumand high-power applications in the L to K bands.

A third class comprises so-called junction circulators which consist of a junction with three or four ports, constituted by regular waveguides, in the center of which is fitted a ferrite rod subjected to a transverse external magnetic field.

Junction circulators belonging to this third class are of interest in that they are of relatively small size, are of compact shape and, in the case of those having three ports, may form Y-junctions whose summetry affords versatility in use. However, circulators of this type have a limited power-handling capacity, chiefly as regards peak power, and modifications which have been made to their structures in order to reduce the dangers of electrical breakdown by inserting an insulator of high dielectric strength between the axially spaced ferrites have not produced satisfactory results.

SUMMARY OF THE INVENTION The object of our present invention is to provide a new and improved junction circulator with a compact waveguide structure which is capable of sustaining high mean and peak power levels.

In accordance with the invention we provide in a junction of at least three rectangular waveguides having axially spaced ferrite members such as discs, fixed to opposite inner wall surfaces of the structure at that junction, a metal plate spanning the whole area of the junction substantially in the magnetic midplane thereof. Mounted on opposite sides of this plate, in line with the axis of the junction are additional ferrite members spacedly confronting those on the inner junction walls, the whole assembly resulting in a junction circulater equivalent to a stack of two junction circulators of reduced size which are electrically connected in series.

BRIEF DESCRIPTION OF THE DRAWING The above and other features and advantages of the present invention will be described hereinafter in greater detail with reference to the accompanying drawing in which:

FIG. I is a front view of a prior-art junction circulator;

FIG. 2 is a plan view of the conventional circulator of FIG. 1;

FIG. 3 is a front view of a circulator according to the invention;

FIG. 4 is a plan view of the circulator shown in FIG. 3;

FIG. 5 is an isometric view of a circulator according to the invention; and

FIG. 6 is a diagram of a four-port circulator embodying our invention.

SPECIFIC DESCRIPTION The conventional junction circulator shown in FIGS. 1 and 2 is a three-port circulator defining a Y-junction I with three arms 60, 70, formed by waveguides of rectangular cross-section. On the axis 2 of this junction are positioned two spaced-apart ferrite discs 3 and 4 which are subject to a transverse magnetic field generated by a magnet 5. The operation ofa circulator ofthis type is known and will merely be summarized. The ports of the Y-junction, designated 6, 7 and 8, are angularly equispaced in the magnetic plane of the waveguide structure. Microwave energy entering through port 6 leaves through port 7 and energy entering through port 7 leaves through port 8.

In order to minimize internal reflections in such a circulator, the impedance of the waveguides must be reduced at the point where the ferrites are situated. Rectangular waveguides in current use are standarized as to the ratio of their sides, known as aspect ratio, which is of the order of 2 I so as topropagate the TE 10 mode. To reduce the impedanceof the waveguides, it-is necessary to reduce their effective height. This reduction is conventionally achieved by inserting into the junction metal plates 9 and 10 which form an impedance transformer. These plates are placed against the broad walls of the structure at the junction and the ferrite discs 3 and 4 are bonded to the confronting plate faces. It is clear that the insertion of the plates unavoidably re duces the distance separating the ferrite discs and increases even more the danger of electrical breakdown at this point. The power-handling capacity of such a prior-art junction circulator is therefore limited, which thus imposes a considerable limitation on its possible uses.

Our studies of junction circulators of the type described with reference to FIGS. 1 and 2 have shown that, in order to match the junction in a satisfactory way, the impedance of the guides should be reduced to substantially half its normal level, which means that, at the junction, the aspect ratio between the magneticplane and electric-plane sides of the rectangular waveguides should be established at about 4 l. Observing this ratio results in a type of circulator which is shown in FIGS. 3 and 4 and which effectively represents two low-impedance-junction circulators electrically connected in series.

In FIGS. 3 and 4, which show an example of a circulator according to the invention, elements equivalent to those of FIGS. 1 and 2 carry the same reference numerals. These elements are the junction proper l, the ferrite discs 3 and 4, the magnetic-field generator 5 and the ports 6, 7 and 8 at the ends of waveguide arms 60, 70 and 80.

Into this standard Y-junction is inserted, at a level of the longitudinal plane of symmetry, a metal plate 11, which has the effect of dividing the junction and the standard waveguides of side ratios 2 l into two junctions with associated guides of reduced height. This plate extends all-around the discs 3, 4 and spans the whole area of the junction if desired, it may also extend beyond that area into the arms to form magnetic-plane partitions therein, as shown for example in FIG. 5.

There are thus obtained two waveguide junctions of reduced impedance; two ferrite discs 12 and 13 are centered on the axis of the junction and are carried on opposite sides of the conductive partition 11, these discs being coextensive with the discs 3 and 4 respectively confronting same. We thus obtain, in effect, two stacked circulators which are electrically connected in series. They may be easily matched without impedance reduction since they are already made from lowimpedance guides. An impedance transformer such as the plates 9 and 10 of FIGS. 1 and 2 is no longer necessary.

It will be noted also that, in the case of each constituent circulator, the distance between the first and second pairs of ferrite discs 3, 4 and 12, 13 is approximately the same as in a usual circulator as shown in FIG. 1 and its power-handling capability is therefore not very different from that of such usual circulator Since each of the circulators only receives half the incident energy, the total permitted power in an assembly of two stacked circulators of reduced dimension is practically twice that of a conventional circulator.

This embodiment also has a better mean powerhandling capability since the surface area for heat dissipation is practically doubled. It may further be seen that in each constituent circulator the ferrite operates under improved conditions since it is subjected to only half the incident power, which reducesnon-linear effects in the material.

FIG. 5 shows a diagrammatic view in isometric perspective of a circulator assembly according to the invention produced by stacking two identical circulators of reduced dimension along the axis 2 perpendicular to the magnetic plane. This Figure, in which the plate 11 extends over the whole of the junction and the associated arms, also shows how the energy of a wave having the fundamental mode TE 10 is distributed when it is applied to port 6. FIGS. 4 and 5 both illustrate the 'par tition 11 as bounded by edges perpendicular to the centerlines of the several waveguide arms, and therefore to the direction of wave propagation, in contrast to the triangular plates 9, 10 of FIGS. 1 and 2.

In the above description we have discussed Y- junctions having three ports. The principles of the invention apply equally to T-junction circulators. Similarly the number of ports which may be envisaged is not limited; thus, for example, a four-port circulator may be obtained by cascading two three-port circulators, as shown in FIG. 6, the two circulators 14 and 15 with ports 16, 17, 18, 19 being interchanged by a common waveguide arm 20. A wave applied to port 16 is received at port 17, a wave applied to port 17 is received at port 18 and a wave applied to port 18 is received at port 19. In this case each circulator l4 and 15 has the construction in accordance with our invention described with reference to FIGS. 3-5.

It should be understood that the concepts of our invention are not limited to the specific embodiments herein shown and described but departures may be made therefrom within the scope of the appended claims without departing from the principles of the invention and without sacrificing its chief advantages.

What is claimed is:

l. A circulator assembly comprising:

a waveguide structure with three coplanar waveguide arms of rectangular cross-section merging in a magnetic-plane'junction centered on an axis perpendicular to the magnetic plane;

a pair of first ferrite members spacedly mounted along said axis on opposite inner wall surfaces of said structure;

a conductive partition transverse to said axis mounted in said junction substantially midway between said wall surfaces, said partition extending all-around past said ferrite members and spanning the entire area of said junction;

a pair of second ferrite members coextensive with said first ferrite members on opposite faces of said partition, said first ferrite members spacedly confronting said second ferrite members; and

magnetic-field generating means in line with said axis mounted externally on said structure.

2. A circulator assembly as defined in claim 1 wherein said first and second ferrite members are discs.

3. A circulator assembly as defined in claim 1 wherein said partition is bounded by edges perpendicular to the centerlines of said waveguide arms.

4. A circulator assembly as defined in claim 3 wherein said edges lie at the ends of said waveguide arms proximal to said junction.

5. A circulator assembly as defined in claim 1 wherein said partition extends beyond said junction into said waveguide arms.

6. A circulator assembly as defined in claim I wherein said waveguide arms have aspect ratios of substantially 2 l.

7. A circular assembly comprising two cascaded waveguide structures each including:

three coplanar waveguide arms of rectangular crosssection merging in a magnetic-plane junction centered on an axis perpendicular to the magnetic plane, one of said waveguide arms being common to both structures;

a pair of first ferrite members spacedly mounted along said axis on opposite inner wall surfaces of the respective structure;

a conductive partition transverse to said axis mounted in said junction substantially midway between said wall surfaces, said partition extending aIl-around past said ferrite members and spanning the entire area of said junction;

a pair of second ferrite members coextensive with said first ferrite members on opposite faces of said partition, said first ferrite members spacedly confronting said second ferrite members; and

magnetic-field generating means in line with said axis mounted externally on the respective structure. 

1. A circulator assembly comprising: a waveguide structure with three coplanar waveguide arms of rectangular cross-section merging in a magnetic-plane junction centered on an axis perpendicular to the magnetic plane; a pair of first ferrite memBers spacedly mounted along said axis on opposite inner wall surfaces of said structure; a conductive partition transverse to said axis mounted in said junction substantially midway between said wall surfaces, said partition extending all-around past said ferrite members and spanning the entire area of said junction; a pair of second ferrite members coextensive with said first ferrite members on opposite faces of said partition, said first ferrite members spacedly confronting said second ferrite members; and magnetic-field generating means in line with said axis mounted externally on said structure.
 2. A circulator assembly as defined in claim 1 wherein said first and second ferrite members are discs.
 3. A circulator assembly as defined in claim 1 wherein said partition is bounded by edges perpendicular to the centerlines of said waveguide arms.
 4. A circulator assembly as defined in claim 3 wherein said edges lie at the ends of said waveguide arms proximal to said junction.
 5. A circulator assembly as defined in claim 1 wherein said partition extends beyond said junction into said waveguide arms.
 6. A circulator assembly as defined in claim 1 wherein said waveguide arms have aspect ratios of substantially 2 :
 1. 7. A circular assembly comprising two cascaded waveguide structures each including: three coplanar waveguide arms of rectangular cross-section merging in a magnetic-plane junction centered on an axis perpendicular to the magnetic plane, one of said waveguide arms being common to both structures; a pair of first ferrite members spacedly mounted along said axis on opposite inner wall surfaces of the respective structure; a conductive partition transverse to said axis mounted in said junction substantially midway between said wall surfaces, said partition extending all-around past said ferrite members and spanning the entire area of said junction; a pair of second ferrite members coextensive with said first ferrite members on opposite faces of said partition, said first ferrite members spacedly confronting said second ferrite members; and magnetic-field generating means in line with said axis mounted externally on the respective structure. 